This invention relates to endoluminal medical devices for implantation within the human or animal body for treatment of endovascular disease. In particular, this invention relates to stents for use with endoluminal medical devices having a novel attachment structure.
The functional vessels of human and animal bodies, such as blood vessels and ducts, occasionally weaken or even rupture. For example, the aortic wall can weaken, resulting in an aneurysm. One surgical intervention for weakened, aneurismal, or ruptured vessels involves the use of stent grafts to replace or repair the vessel. Stent grafts may be formed from a tube of a biocompatible material in combination with one or more stents to maintain a lumen therethrough. The stents are attached to the graft material in a number of ways, including by suturing the stent to the graft material.
It is preferable that these prostheses seal off the failed portion of the vessel. For weakened or aneurismal vessels, even a small leak in the prosthesis may lead to the pressurization of or flow in the treated vessel, which aggravates the condition the prosthesis was intended to treat. A prosthesis of this type can, for example, treat aneurysms of the abdominal aortic, iliac, or branch vessels such as the renal arteries.
The above-described examples are only some of the applications in which endoluminal devices are used by physicians. Many other applications for endoluminal devices are known and/or will be developed in the future. For example, in addition to the use of stents and stent-grafts to treat vascular stenosis and aneurysms, similar procedures may also be used to deploy vascular filters, occluders, artificial valves and other endoprosthetic devices.
Migration of endoluminal devices from their location of implantation may present a significant problem where the prosthesis is subject to the forces of blood flow, especially on the arterial side. For example, the prevention of migration is extremely important and challenging when placing a stent graft to repair an abdominal aortic aneurysm (AAA) where downstream migration of the device can result in the aneurysm no longer being excluded. Unlike surgically placed grafts that are sutured into place, only the radial forces of the stent are available to hold the prosthesis into place. If the aneurysm is no longer intact or subsequent rupture occurs, consequences may be dire.
To alleviate or obviate migration, attempts have been made to secure the device in place with a series of barbs or hooks that extend outward from the main body of the device, typically at its proximal end, either by attaching them to the stent frame with solder or by some other bonding technique, or to the graft material, typically by suturing. These barbs can be attached to the stent wire by wrapping, chemical bonding, welding, brazing, soldering or other techniques. For example, one embodiment of WO98/53761 utilizes barbs that extend from the suprarenal fixation stents to engage the aorta wall.
It has been observed that sutures attaching barbed stents to the graft material are subject to breakage due in part to the flexibility of the graft material and the considerable pulsatile forces of arterial blood acting on the device. These forces have been known to directly contribute to the detachment between the graft portion and anchoring stent.
It has also been observed that barbs separately attached to the stent frame are subject to fracture, detachment, or other failure, especially when the forces become concentrated at a particular location along the stent graft. Simply making the barbs stronger to prevent fracture can result in increased damage to the anchoring tissue. Furthermore, adding rigidity to any outward-projecting barbs may compromise the ability of the device to be compressed and loaded into a delivery system. The use of multiple barbs can prevent undesirable migration of the device, especially if there are a very limited number of barb failures. Yet, while a single barb failure should not result in the migration of the device and may not represent a problem clinically, barb fracture or failure is nevertheless currently classified as an adverse event that manufacturers seek to avoid.
Another solution to the problem of barb failure better was disclosed in U.S. Pat. No. 7,081,132 to Cook et al. There, the barb included a basal portion that joins the strut of the prosthesis from which the barb extends, and a stress-dispersing region located between the anchoring portion and the basal portion, usually closely adjacent to the basal portion, that is adapted to better distribute stresses and strain caused by forces acting on the barb, thus preventing their concentration at a particular point which would increase the likelihood of barb fracture. The stress-dispersing region may comprise a coil of a greater pitch than the windings of the basal portion, a coiled loop bend, U-shape bend, or other series of bends. However, this barb design still requires the use of a separate wire portion soldered, welded, or mechanically attached to the strut of a stent.
Typically, stents are manufactured from a single piece of material, and they are sized depending on the size of the vasculature of the patient receiving the stent. However, the process for creating the stent is time-consuming and makes it more difficult to cater to different patient sizes.
Accordingly, there remains a significant and unsolved need for a barb configuration that reduces barb failure and has a simple structure that does not require attaching a separate barb structure to the strut of the stent.